The question of “engagement vs boycott” is as old as all questions related to human relations. And Israel’s Washington ambassador, Michael Oren, has been pondering it again.

Next week, the “pro-peace, pro-Israel” group J Street will hold its first national conference in Washington. Mr Oren was invited to speak, and soon realised that, more than an invitation, this was a trap.

The group is no doubt pro-peace, but its “pro-Israel” credentials are being increasingly questioned. The embassy’s spokesman, expressing what Mr Oren seems to believe, had said that “while recognising the need for a free and open debate... it is important to stress concern over certain [J Street] policies that could impair Israel’s interests”.

J Street, on more than one front, tilts quite radically to the left, perhaps even to the left of Mr Obama.

Clearly, it is much to the left of Israel’s government and Israeli society. The head of opposition, Tzipi Livni, had also declined an invitation to speak to the group. J Street will find support among Israelis only at the fringes of Israel’s political field.

Inviting Mr Oren, though, was a win-win move. The group had already secured some big names — National Security Advisor Jim Jones, some senators and congressmen sympathetic to J Street, or eager to please elements of the Democratic Party. So Mr Oren was burdened with a problematic decision.

Addressing the group would give it the “legitimacy” it seeks, a stamp of approval from the Israeli government, or at least public acknowledgment that it now merits attention.

A decision not to attend would give the group what it likes most: another opportunity to say that it is shunned and that there is a scheme to “silence debate” on Israel in the US. J Street has been marching to this tune for 18 months, gaining sympathy mostly from the unaffiliated and the uneducated.

And indeed, when Mr Oren was slow to react to the invitation, J Street took to the airwaves, urging him to attend and contending that “engaging this part of the community and finding common ground, even as we differ on policy, would be an important step for Israel in ensuring continued, long-term and deep support for Israel across the breadth of our community.”

When he later finally announced that he was going to decline, and send a lower lever official to “observe” the conference, the group said that the invitation is still “open”. Never drop a winning card.

But Mr Oren, as ambassador, had more to consider than the important Jewish-progressive constituency that J Street’s director Jeremy Ben-Ami was talking about. He needed to consider the watching congressmen, those still undecided about J Street. If Mr Oren had attended, they would have been able to attend without the fear of being negatively labelled by pro-Israel activists.

He needed to consider the fact that the strengthening of J Street would weaken the unified voice of the more centrist advocacy groups. He needed to consider the fact that this game, like most Washingtonian games, is not just about the “issues” — in this case Israel and the peace process — but also about power.

Does he want to be the one making it easier for J Street to gain power? Definitely not.

Trouble is that the dilemma was a tricky one, and Mr Oren can’t be assured that either decision would hurt J Street more than it would help him. A trap.